In recent years it has become increasingly popular to provide vehicles with the ability to convert between two-wheel and four-wheel drive. As popularity has grown, so to have the many ways of affecting conversion. In one example there is a permanently driven drive line segment to the rear wheels of a vehicle, and a part-time driven drive line segment to the front wheels. The part-time drive line segment is simply disconnected/decoupled from the engine's drive shaft at the transmission or transfer case and that segment is rendered passive (undriven). There is often a second point of disconnection which may be at or near the differential (a center disconnect) or at both wheels.
There is a mechanical action that takes place to achieve each connection and disconnection as contemplated herein. Two shafts or drive line segments are in close relationship and a clutch ring that is permanently coupled to one shaft is slidable into engagement with the other shaft to couple (connect) the shafts and is slidable out of engagement with said other shaft to decouple (disconnect) the two shafts.
The sliding movement is achieved by what will here be referred to as an actuator. The actuator can be many types including, e.g., a shift lever, manual or electrically driven, it can be cam actuated and it can be pneumatic actuated. The present invention is directed to pneumatic actuators for clutch ring actuation.
Pneumatic actuators in general are not new. A pneumatic actuator is disclosed in U.S. Pat. No. 4,627,512, issued Dec. 9, 1986. This actuator was applied within a wheel hub for connecting/disconnecting the wheel from an axle. Another pneumatic actuator is disclosed in U.S. Pat. No. 5,044,479. One embodiment of this patent applies to the wheel hub of a vehicle and connects/disconnects an axle from the wheel hub, and another embodiment applied at a juncture between two axle portions located between the wheel hub and differential.
The pneumatic actuators as disclosed in these patents, and other similar actuators, function as claimed but they do have problems. In the '512 patent, the air chamber is formed between components that have relative rotation making sealing difficult. Furthermore, the negative air pressure typically available for actuation, e.g., from the vehicle's exhaust manifold, is limited and the designs of both the '512 patent and the '479 patent can be inadequate to produce the desired actuation.
For the above reasons at least in part, the pneumatic actuator for the clutch ring has not gained a high degree of acceptance. The objective of the present invention is to provide an improved pneumatic actuator that avoids the above problems.